Apparatus for regulating power used by pulp grinders



8 Sheets-Sheet 1 L. A. COLE APPARATUS FOR REGULATING POWER USED BY PULP GRINDERS mbz: umozw nia March 13, 1951 Filed Junev, 1948 m i. m

March 13, 1951 2,545,260

L. A. COLE APPARATUS FOR REGULATING POWER USED BY PULP GRINDERS Filed June 3, 1948 `8 Sheets-Sheet 2 /73 J H /72 No a, J o o /7/ o J J C' /6 l l 'o V 55 i o 17a/74 W /0 /ff 77 o Hf@ l nf@ A I l l, Ill N l l @o HK I l @a `l l Q l 1L D G Il ll|\\ /6=/ 30a aNQEN-ron.

AT1-YS March 13, 1951 L.. A. COLE 2,545,260

APPARATUS FOR REGULATING POWER v A IUSED BY PULP GRINDERS Filed June 3, 1948 8 Sheets-Sheet 5 M 49 s 47 22 z/ 38a 20 /9 W @D c@ 2s 'E I @$6.4

\ LA. com d March 13, 1951 l.. A. COLE 2,545,260

APPARATUS FoR REGULATING PowER USED BY PULP GRINDERs a sheets-sheet 4 Filed June 3, 1948 um 9m. m Wr Nw Mv M $5 Sm T Aim.

tNvENToll LNA. COLE- Ar-r'ys March 13, 1951 A. coLE- APPARATUS FUR REGULATING PowER USED BY PULP GRINUERS Filed June 3, 1948 8 Sheets-Shea?I 5 INVENTOR L. A COLE A-r'r YS March 13, 1951 L. A. COLE 2,545,260

APPARATUS FoP REGULATING POWER USED BY PULP GRINDERS Filed June V3, 1948 8 Sheets-Sheet 6 HH/W 90 ATT'YS 0 6 2, 5 4 5 2 R m o wm mm EMm LW@ @s .WY L B CMD` www mn P P A 1 5 `9 l .uw l im 8 .Sheets-Sheet 7 Filed June 3, 1948 J u., f m, J w L 7 A m" f N H f E m v A A W, 7 J w W m L 3 f 8 3..: W G m M/ W F8 Mw 9 /V u W MO ,2o 6 M m March 13, 1951 L. A. coLE APPARATUS FOR REGULATING POWER USED BY PULP GRINDERS 8 Sheets- Sheet 8 Filed June 3, 1948 NVEHTR L.A COLE ATT y sl/ Patented Mar. 13, 1951 l OFFICE APPARATUS'FR REGULATIN G POWER USED BY PULP GRINDERS k LorneA. Cole, Brantford, Ontario, Canada Application June s, 194s, seria1No.3o,94s (o1. eno-97) 12 Claims.

1 'This invention relates to Amethod and apparatus for regulating the power used by 'pulp grinders employed by the pump and paper industry for grinding logs 'against motor driven grindstones.

yThe usual arrangement'ofpulp'grinding devices involves a synchronous grinding motor carrying a pair of grinding wheels at either end, and mounted in pockets, each grinding wheel Yo1' stone having a magazine on either side adapted to receive logs. in vconjunction with each magazine having a grinder or pressure foot which is actuated thereby and forces the logs against the grinding Wheel. The system employed for actuatingthe hydraulic pressure cylinders in the conventional arrangement includes a reserv-oir of Waterand a pump which Y provides high-pressure water from the reservoir, which passes through a governor such as that disclosed in my former Patenti 387,960 in Canada. Thus, all hydraulic pressure cylindersare operated fromone highpressure line controlled from such'agovernor in 'prior arrangements.

The governor disclosed in Canadian Patent 381,960 was particularly designed to smooth out power or load peaks which occurred when certain conditions arose due to changing load between the various grinder feet of say, a fourcylinder system employing two grinding wheels.

This formerproposal has been generally/satis-l factory but it does not avoid` some substantial fluctuation in lpower consumption due to the sudden retiring 1 of a pressure foot after the completion of a grinding stroke or the sudden application of pressure on the logs at the beginning of a grinding stroke. Such iiuctuations are quite severe if two pressure feet complete their4 grinding operation j together or substantially simultaneously. A further disadvantage in conventional pulp grinding systems is that great diiculty is encountered in clearing the magazine when logs become jammed between the pressure foot and the grinding wheel. It is therefore a main object of the present invention to provide a control means for a pressure cylinder and operating in a hydraulic syssigned to control the operationfof a` pressure cyll inder, i. e., to control the piston of the' cylinder by means of a control unit operating with a lowpressure system, iny addition to the priorv highpressure system.

A pressure cylinder is mounted.

` provide Va control unit having means whereby.

pressure fluid for initial control of the pressure foot piston of the pressure cylinder which the control unit serves, in its advancing and retiring movement and to cushion the piston at the ends of its stroke.

'A stm further object 'of the invention is toprovide a control unit as before which includes by a pressure foot piston under load by means. of a variable back pressure from the low-pressure line applied to the front of the piston.

@A still further object of the invention is to the same may be manually controlled inits operation'and further including means whereby the pressure foot of a cylinder may be halted at any position so that the magazine of its pressure= cylinder may be cleared. Y

.A still further object of the invention is to provide electrical means governing actuation of the valves of the present control unit actuatable` by limit switch means operatively. related withl the movement of the pressure foot piston of its' pressure cylinder and including an arrangement whereby the electrical circuits of a plurality of control units according to the present invention,

are related in series electrically whereby only. one control unit may cause actuation of its pres-A sure cylinder at any one time.

With these and other objects in view, the invention generally relates to a method of controlling power urry in pulp grinder units compressure fluid wherein the low-pressure uid is introduced at either end of the pressure cylinder tcLdrive the piston'byapplying pressure at either end. When the piston is advancing, communication between theA front end ofV the pressure cylinder and the sump is severed, not later than substantially simultaneously with the cutting oil of pressure fluid from the back end of said pressure cylinder, thereafter low-pressure fluid is -1 introduced into the front end of said cylinder and the rear end thereof is placed in'communi- A further object of the invention is to provide-5 cation with a sump substantially simultaneously whereby said piston is retarded within said pressure cylinder. The retired limit of travel of said Ipiston is cushioned by severing communication between the rear end of the pressure cylinderand the sump,- and at aboutvthe same time shutting off the supply of pressure iiuid from in front ofthe piston. The front end Vof the pressure cyl- 6 a predetermined Value the high-pressure fluid isf communicated to the back end. of' the.v pressure. cylinder to drive the piston under load.. method is carried out by way of practical apparatus embodying a control unitf-designedto=cor1.l trol the operation of a pressure; cylinder` of.v aipulp grinder in which the piston of said cylinder is adapted to be driven by hydraulic pressuree derived from a low-pressure line and a highpressurelline; and comprising a plurality ofsoper.- f atively 'related'valven meansfcertain of .which aree in.; communication. with.. the. back end of said; cylinder, andy others zof` whichA are in communication with the front end of said cylinder; The` Valve.:meansfare designed to placefthe front end ofsaidzcylinder incommunication with the .lowF-e pressure line;to.cause.a retiringof the piston, and.' means. are :provided :for-'actuation .of theeplurality, of: valves: in predetermined.. order to: urge` said'. piston forward after it has;completeditsretiringl stroke;=. Meansare; also included. for :placing said high-.pressure line in, communication. with the: backendzof said: cylinder. to. apply highepressure` to: said piston.. when the; pressure behind' said piston approaches. a'. predetermined: value;4

In addition,.the3presentinvention incorporates4 means .whereby the; pressure. foot-1 of a cylinder mayvbeuhaltedzat any position',v and;the. remaining" pressure` feetuof.. the..A systemY continue; operating... Each'. control unit; designedf to; operate;v autov matically` and. includes:.i.electrical relay. means in v anelectrical circuit; inter-relating'.- various: conM trol units in any one systenriwhich"govermthe.: operationioff the valves;V of each. control .unit by virtue-.fof limitiswitch Voperable .byeachrpressuref foot'u or4 pistoni of; each` pressures cylinder.: The? relay means lof .the Ycontrol circuit arespia-ced.electrically inrseriesA whereby only oneocontrol:n uniti may. be.v actuated Lto. retire itsfpressure cylinder piston .at.1any; one time; In `the r event. thatlthe` electrical systemVv breaks down'- for anyireasom. meansT are zincluded': wherebyrthe: systemlma;7 'bei manually operated; thus; assuming-i.v thatzhighf-Y pressure and low-pressure-water 'orffluidis ob.-

tainable from thesreservointan .operatorrma'yzfby operationiof au single-:valve;:. continue-operatingra particular` pressure cylind'erg. Means'. are; also; includedlfor. varyingpthe.:grindingipressureeto:bei applied bysthe pressure.cylinder-operated '.by, the .-1 control .uniti 'f by applying an adjustable: pressure, head: at the :front of the: piston` ofithe pressure: cylinder in opposition. to r the: driving@y pressure: applied tothe rear of the-:pistonsy Thisback-f pressure, that is. to ,say, .the pressure "applied J in front of the .piston .maybe, different-asl.betweenY4 all four cylinders of asystem. causing; the .governor, such. as .described `in Canadian .Patent l. No.y

387,960, to automatically apply fourA dilTere-nt. effective pressures.

It will be apparent that the-.control unit=of the. present invention is .designed for use with asingle.A pressure cylinderof a pump grinding, system and.. therefore, it will be necessary to employfwith... each pressure cylinder of Such a system a control. unit. having the advantages above outlined-and. hereinafter more .particularly described.

Reference .is therefore; made to. the.. accome panyingY-drawings .wherein Figure .1 is-afdiagramematic. view of af. control. unitaccording, to ,ther

present invention, connected between a governed high pressure fluid supply from a fluid reservoir and a pump grinding pressure cylinder. This diagrammatic"illustration is. intended'i to infer that anopposedpressur cylinder may be connected to a different control unit (not shown) which is connected in parallel with the control unitshown,` to;the.governor controlled fluid pressure system.

Figure 2 is a perspective view of a control unit of thepresent invention connected to a pressure cylnderof. apump. grinding unit.

Figure 3 is a diagrammatic view of a pressure cylinder showing the hydraulic means controlling operation of the same and involves a plurality of valves1vA-,.BG, D.,-an^d,E;. which comprise,v the control. unit.. shown.e in Figure. 2 when mounted: upon '.the control 1ste/nd.. in conjunction with cer't tain.;` operating.: valves also.` diagrammatically:I` shown. In this figure, the piston is; shown in the advancingposition with. the operative positionsof the felementsfof `va'lvesA to E inthe relative operativepositon Figure.-lfisaffurtlfreroperative view of Figure 3"4 showing thewpositionsof thefelements :of valves 'A- toEzwhen thepistonfisrretirin'g in thepressure` cylinder:`

Figurefishows the? position i ofther communi.- cating; passagesA within; a four-way' valve for manual.y operation ofy grindingy inthe event ef current .f failure. infy the; electrical. systemY of 1 the control runit.'

Figure 6V shows tl'iefpositionv of a:four.-wayva'lve;l for: effecting retiring.;` ofithe pistonzof; the. presT surelcylinderv byzimanual roperation Figure 17 isa diasrammariciviewof theiposition: of lthe four-wayvalvein normalpperation .of-.the system as shown in Figuresfandrle.

Figure 8 is a diagramnmticfView:oflthe-.posiV tion: ofi the.four1way. valve:` for-:halting the position ofzthefpressurefoot to.-a1low'clearing oi..tlieY grinding' pocket between the.: pressure.-` foot., and f thegrinding wheel-:oigthea grinding unit;

Figure 9..:iS. electricallschematic of an electrical system?. for four: pressure cylinde'ers,` which varefcontrolledzfby 4four controlffunits. according-to thezpresent inventions. f

ligureelo. is aasectional Viewzof thezpreierred structurecfor;thezBfw/alve or the rD valve of the control-L unit. i

Figure; 11. is impartial! sectional v4view ofthe valvesof `thefcontrol unitlwitl'r' thef topi cover rey movedf.. I

Figure..-12;3is appar-tial. sectionalivi'ew of 'the C valve of the;controliunitshowing acompression spring cylinder mountedlonitheftop of the valve` ofia:typevwhichpislalso mountedon the tops of' therB', .DIandwEJvalvesiatendingfto :force:.the..piston 1 of each valve downwardlywithinithefvalve body* or housingg- FigurexlS ii5.;a .partialfsectional 'View of. the A valvefof the control unit: of therpresentlinverrf tion :showing limit switch means `actuable :by the movement Y of the piston v and which electrically control raising of.B,-C and D Valves;

Figure-14-=is a. partial-sectional View of limit switch.. means operative in` conjunction with. the movement of theepiston-of thepressurecylinderi whchth-e present control unit controls.

Figure 15is..a-side elevation of the: control span whiczh mount-s valves A to E as shown in Fig.- ure Figure :16 lisaafront elevationlof. Figurel:

EgureelSsis-:a View Y' I -8.-l8-of Figure 15,-.also diagrammatically illustrating by chain lines, a

control valve hereinafter referred toas the I valve for controlling the back'pressure on the piston of the pressure cylinder.

Figure 19 is view I9-I9 of Figure 15.

Figure 20 is a sectional view taken on 20-29 of Figure 16.

Referring now t the drawings and particularlyl to -Figure 1, a pulp grinding system is indicated schematically-and includes a control unit of the present invention between each pressure cylinder I0 and the hydraulic terminals II, I2, I3 and -I4 of the well-known pressure system shown in chain lines. It will be apparent that the control unit uses raw high pressure from terminal II, governed high pressure from terminal I2, raw low pressure from terminal I3, and controllably delivers same bymeans of lines I5 and III'toA the front or back of the pressure cylinder Il,dischargel or sump water being returned to the reservoir bymeans of line I1 connecting to terminal I4. It -will be apparentthat a control unit connected in parallel with that shown in Figure vlto terminals Il to I4 may communicate t0 pressure cylinder I8. It is possible therefore, in the hydraulic system to operate as many cylthe line `inders as desired, providing a control unit according to the present inventionis employed to operate each, all control units being connected in parallel hydraulically as regards the supply of pressure uid. I 1

In Figure 2, a control unit according to the present invention is shown comprised of a control stand Ia having mounted thereon and hydraulically operativelyv related, valves A, B, C, `D and E. The top of the control stand communicates by wayv of conduit I6 to the back of the pressure cylinder I0.' Also mounted onthe control stand are magnetic valves, each being of the same design as that disclosed in my prior Canadian Patent 387,961 designated by letters G, H and K. -Irl order to appreciatel the features of the present control unit, it is rst necessary to discuss the operation by reference to Figures 3 toV 9.

In the following figures, as in Figures 1 and 2, like numerals indicate like components.

- Operation.

In Figure- 3, valves A to E aredesignated b-y land operatively connected thereto by a piston arm or rod 2,6, Arrow l21 indicates that the piston is advancingycorresponding to the positions of the valve pistons I9 to 23 indicated in this figure.

[I3 by way of line 45 as indicated in Figure 1.

6? i feeder line and delivers return water byway of line 32'to terminal I4 as indicated also in Figure 1. 1 Forthe desiredoperation of advancing the piston in Figure 3,-the electric-al current is shut off in the magnetic valves K and G but the current is on in the magnetic valve H, the electrical functions to be described hereinafter, but assumed for the present. It will be evident therefore, thatr the control feeder line will assume normal pressure since itis placed in communication with the reservoir of Figure 1. Valves A to E therefore, may be assumed as being in the down position shown, in which instance governed high pressure will be flowing through the globe valve 33 (see Figure 1) from terminal I2 to the upper chamber 34 of the A valve. The A valve being opened; the fluid circuit `will be complete therethrough and high pressure fluid will be injected by way of line I6 to the rear of the pressure cylinder I0. The latter line is also in communication with the upper chambers 35 and 36 of vvalves B and C as indicated by lines 31, 38 and.

39; the B valve' beingclosed, a branch of the high pressure fluid will vflow through -the C valve and; pass by way of lines 40 and 4I to the upperchamber 42 of thefD valve. A check valve 43 prevents the high pressure from flowing in the direction of the globe or gate valve 44 which is in communication with the low pressure supply or terminal It will be apparent therefore, that the high pressure will ensure closure of valves B and D at this point in operation, but that no pressure is necessarily dissipated in accomplishing this function.

It will be assumed that fluid is within the pressure cylinder in front of the piston and therefore, that as the piston proceeds forward fluid will exit from the cylinder by way of line 46 which communicates to the lower chambers of the valves D and E by way ofV lines 41 and the relief valve I respectively. kThe E valve being open and assuming that the I valve is open, this waste fluid will pass through the E valve and into the return line 48 which communicates with the lower cham-- 5' ber' 49 of valve B and also with the valve 50 which High pressure from terminal I I, that is, directly Y from the pressure pump, passes through the needle valve 28 to the magnetic valves K and G and thence to the control feeder line 29. The latter communicates to the bottom of valves A, B, C and E directly; but passes through aJfourway Valve 35 to the bottom of the D valve. The emergency feed valve 3l communicates with the valve Sil' and also with terminal II (see Figure 1) but for normal operation is closed. The fourway valve also has a return line I1 extending therefrom and connecting to terminal I4- (see Figure l) In the position ofthe four-way valve shown, b'othinFigures 3 and 4, the control feeder line communicates directly therethrough tov the 'bottom'of the D valve for normal operation. The

magnetic valve H connects from the control s.

isfin communication with line 32, which inrturn communicates -to terminal I4 (see Figure 2). Valve 5) being open, the fluid will return to the reservoir as the piston 24 proceeds forward in the cylinder I0. It is important to note that the valve A has a heavy spring represented by arrow 5IZ tending to pull the piston i9 thereof into the closed position at all times. The remaining valves B to E have similar springs but which act to force the pistons thereof downwardly in each case. Valves'B and D have heavy springs 52 and 53T whereas yvalves C and E have light springs 5ft and 55. Y Y

In Figure 3, the piston is shown advancing in; the cylinder l0 and as it approaches the end of its grinding stroke a limit switch mounted on the cylinder I0 (see Figures 2 and 14) is actuated, causing the K valve to open and the I-I valve to close. The K valvefhas a small orifice of about 5%000 of an inch in diame'ter so that pressure will build up in the control line gradually. All valves have high pressure fluid in their upper chambers with the exception of the E valve which has a light spring and therefore the piston 23 of the El valve will rise `first.l As a result, -the pressur'ein front of thepiston 24 ofthe -pressure cylinder will build up as-thepistony advances' utilthe pressures, on either iside of' the 'piston arevs'ubs'tantiallyf equal." vThe A' valveI has a heavy spring tending' to pull its piston or closure At his ,pei-nt, Yew@ eleees, aetueteelwh dine, @hawaen eey ee @E t springt@ mf-g ,seme enevv ehe eee@ 't oeee next' @nemesi Figure '7 ieeiieeteseieseemetieellmhe position of the four `ay valve 30 for normal 0peaton, in which case-the high pressure valve 3| lefeloeedee previonslyvdeseribed.with leeeeneeto 00 .Eignres '.3 and f1. However; ,when logeheegwse jammed between the pressure :feet @215 md th er' ddee, stelle, itis neeeeery ier ene@ teme remue .the lemme@ meherieL I--preYide .meme orlincremeneelly mevfiee me ereseme @et back,.- ee .is evideeeegl inie Send .ilewlvmg xthe rourewey-velve 3Q. *'Ehelkliehvpeseu! QV. vie 3141s elOSed, eyed lthebeiwri -ef the D valve ie placedfemmunioetionwith line JJ.. Itwisllbe www-reis, in ehember 34 of tbe i. new ,L1-eh ,preseure gradual-1y ,limpeese hen the nresexme rr erpeeheeeefalieee fy; eerelllf 'eeef-teryrlle epprpximatel the messer ometheiow 1mg itefleemel.eleleefiepere messereteemirlel Assemes A 7,5 eeeeeiee@ Electrical circuit ate four pressure cylinders. Four control circuits are shown interrelated in Figure 9, each of which `governs the operation of the G, H and K valves of each control unit.

Referring to the figure therefore, the electrical V lines 51 and 51a connect to a conventional current source (not shown) such as a 110-volt direct current supply line. ,A bank of relays 58 and the magnetic valves 59 comprise the necessary components for effecting operation of'one control unit. The relay bank 58 has an energizing coil 60 having one end connected to the line 6| which connects through double pole switch 62 to the line 51a. The relay'arm 63connects `from'its pivot end 64 to the line 6| as shown. The other end of coil`60 connects by means of line 65 to line66 which passes through limit switch means 55 to line 61 which connects to double pole switch 62 and thence to line 51. It will be assumed, for the purposes of discussion of one control'unit,

and the relays'and magnetic valves in respect thereto, that lines 65 and 66 are connected elecv`|',rica`lly. The arm 63 of the relay is normally Y closed 'with contact 58 which'c'ominunicates by "line 69 to the solenoid 10 of the H valve, the other sideof' the solenoid being connected' to line '61 if as shown. Contact .1| connects by line 12 to the* solenoid 13 of the K valve, the other Vside of the solenoid being connected to line 61. Line 12 also and hence line 51, in which case the magnetic valvel-I will be open.- This corresponds to operation diagrammatically shown in Figure 3, since it will be-app-arent that there can be no current contact 1 I.

flowing in the solenoid 13 and 14 as terminal 1| makes no connection with the relay arm |53.`

Howevenassuming lines 65 and 66 are electrically connected, it will be apparent that when the limit switch means 55 is closed, a coil 60 will be energized causing the arm 63 to engage the be immediately energized causing that valve to [open and when the A valve closes, closing limit j switch 56, the solenoid 14 of the G valve will be energized to open that valve 'at the same time arm 63 opens contact 68 closing H valve.

The above description relates to the necessary electrical means employed for the operation'of 'fone control -unit where it is `desired that each control unit operate entirely I independentv of the other.

However, upon referring to' Figure 9, it will be apparent that only onerelay coil can operate at any one time Vin a multicylinder, multicontrol system and therefore the maximum load change which the governormust compensate for issubstantially only that experiencedwiththel changing load conditions in one pressure cylinder ata time.

In order to accomplish the desired result therefore, tis necessary to mount a number of Arelay arms in conjunction with each relay coil corresponding to the number of other cooperating Y control units.

K Thus, the relay bank 58 has three furtherrelay arms 15, 15 and 11 as do the rearginine relay banks it-5811aneieoiih@icm Y The solenoid 13 Iof the K valve will f control vunitsy'stemi It was assumed above that lines 65 and 66 were electrically connected and Vthis requirement'must be met for each relay bank and cooperating valve unit. The relevant circuits can be traced by means of sub-alphabet numbers, rand it will be apparent upon tracing the circuit that the line 65 for instance, connects to the line r66l by passing through three relay arms of three different relay banks -in the series and numbered 15a, 15b and 15e. Therefore, it Will be apparent that the coil 65 could not be energized unless the remainingv coils 69a, 69h and 60e also were not energized. As shown in the gure any one of n coils 68a to 68e could be energized as soon as any on its pressure'cylinder and the movement of the pressure foot thereof. Y

. scribed a workable control-unit system according to vmy invention, one -practical design of the mel Structure -Although it will be evidentthat I have dechanical components of the system is illustrated ,Figure). into the bottomofl the valve.

. and-will be describedv in order to ensure that all features of my invention are'appreciated. It will be noted however, that the design to be described iscapable vof considerable modification and merely representsone :practical form. Y

A The structure of valves A to E will first be descr-ibeii, valves B and D`-being shown insection fin.' Figure l0 lancl` comprising a valve body 18 having upper and .lower'chambers-'IQ ande80 and a lowerl cylinder chamber 8|. An annular valve seat 82 rests in the partition 83 and is adapted to Vreceive thevalve member which extends up-V wardly from thepiston 85. Guide vanes 86 extend downwardly Yfrom the-valve `element 84 to the piston 85. The Avalve body 18has a top 81 fastened thereto by suitable bolts 88 and a central bushing89 having a suitable packing 90 adapted for passage of thecontrol rod 9|- which extends upwardly yfromthe valve closure element 844 as shown. .s Ports 92 and 93 communicate with chambers 19 and 80 respectively'` The val-ve body 18 has a port -94 .at thebottom end for passage of pressure uid fromrthe control feeder line 29 (see Spring meansY (not shown.) `and yet to be described with reference to Figurel2-are included for ensuring positive engagement of the'valve closure element t 'or member 84 with the seat 82,

, Y. Figure-11 showsA theV preferred structure for the E valve in which the body 95 has upper and lower chambers `96 and91 separated by a parti- --tion member 98 having a'central bore adapted to-receivea valve-seating means 99. A conical `valve vmember' IUD-extends upwardly from the valvepiston (not shown but similar to that shown -in Figure l0) fhaving theA control rodv |8| extendv ing yupwardly through the top of the valve (rev movedjfrom the drawing for clarity) to connect I5to spring means Y'designed to provide normal disi the open position and is comprised of'a-body |06 ,hai/ina. errer, enslzlpwergrhambers |01 and |08 VSarnia. Figure fra-:thee A valve-'hase a; port4 at the levier separated by a partition |09 whichlmounts'the valve seat |10. The valve closure memberv II Iis mounted on aplston H2, the latter'being substantially similar toV piston 85 of valves B'andD.

VVValve guide varies i3 extend upwardly' from the I I9', the latterrbeing mounted by suitable legs |20 to' thetcp IIS of the valve by meansV of the top fastening bolts I2I. The spring cylinder H3 has a top |22l which mounts an adjustable screw 23, the latter having at its' lower end, a suitable disc |24 designed to engage one-end of the spring means I|'|. The spring-H1 is held between the discmlZA andplatform ||8, adjustment cf the i compression inthe'spring'fby means of screw' |23 providing afdjflus'gtm'ent` off the `pressure necessary to close-the valve C; l'alvesYV ByD and have similar spring cylinders mounted n a; simiiar manner, which all tend to force their pistons downwardly within the body ofeach valve. vIhe springs of the B and D valves are heavy in' com- 'pa-risen tc the compression vof the springs in the C and E valves- All valvesB to E have' av port in the bottom end of the body for communication with the control feederV line 29 asvr shown in Figures',v lY and 10. As' fou-nd in the`w consideration 6l valves B, 'D and-E, the C1 valve body HJG, has ports F24 and |25 communicating with the upper and lower chambers I* U1 and Hi8Y respectively. I

The structure of the A valve is shownin Figure I3 and is comprised of' a valve body |26 having upper and lower Vchainb'ers `F21 and |28. The structur shown here is' simi-lar toy that* described with respect to tlie E valve Figure Vllwitlf'l the exception that communication is-provid-'ed into theupper chamber |21 by means of a fitting |29, `which extends to theglobeval'vei and high pressure terminal |22 as shownin Figures '1 and' 3 previously described. The lc'iwer clframberv |28 Vl'ias'an exitport |3-Uin the plate ISI; which is Vp're'li'erably mounted as a'separ'ate cornnonentv in the body I 25. 'The control rod' F32 orf the A'valve extends upward-ly' through' the ton F3301 the body and packing' gland |34 to iaidustably Amount `an actuating dise F at its upper: end. lDisc |35 is slidable within the hereof the nspring cylinder A |361 'ha-s suitable legs' HT extending 'for 'fastening to the ton Ili ofthe valve by means ment t4 If. Winn-1i` me cursar-bere maf f' tristan@ Similar tof they construction-Shown in upper endl of' the; spring cylinder |53151 mounts limit y switch means: 56 which-:are encasedr within a suitable? box: lldimountedl cnthe base e' Y |45I 'extending from fixture. tothe springcyl'in'der. Suit- 1.9A shows theisectional: 'detail of't |66: and |161 and'. their commiimiatioiit hshown in Figuresl'ald iviandfcomprises a stand Mhavng a plurality of inner. channelstolpro- Yvde the necessary .communication between the ports o the valves as [shown .inv Figures 3 and .4.

Iii-Figure 15 the A valve sfmounte'd. so thatthe fastened t the stand by suitable boltsfxedn Ythe-bolt holes |49. .Port |48.communicates to the upper chamber 50 which communcatesleby way` of port I5I tothe conduit'l -shownin Figures 2,3 and 4. Chamber |50 also .communicates by means of ports I52andV |5'2a with the-.upper chambers. 'I3-rand ll-of the Band C valvesI respectively. (ReferringV to Figure 3,- thisinvolvesvthe connecting lines3'i,38 and` 3s' extending from line` le) The lower port-*93 oi B valve communieates byway oi-pert lytofthe downwardly extending channell 54 which communicates Yte Vthe Vport |55. The LE valve is mounted so that its port |52 is in'v alignment'with its port #55, the port H33 being in alignment withtlfi'eport-t.

. The channelfl'jg-therefore corresponds 'to-lines 48 -and 38a of Figures v3 and 4. Referring 'to Figure l5 port i'leads to the throughbore |51 (see Figure 1-8) which communicates to1the-I valve by means of suitable" piping |153, indicated in chain lines. The other. side ofathe I valve communicates to the port: |518' Which leads tothe: inner chamber |63 which is iti-communication Withthe ylower portezof'theDvalve Vlziy'rheans of .port Ii (see .Figure 16). V@flamber 'H56 also-cemvwith the downwardlyextending' channel' F64 arid designed to'provdfcommunication iid-cheek vvali/ac3, valve 4W and line sliown in Figures nels 54 and |54A respectively. The and. "'H val-.iles are mc'untedin the through bore'v and teli, the* electrical leads being passeddowh r'dly througlrthe open'. chamber PTE and passing' by of suitable-cables (not shown? for approal suitabl'` pendant arm 'I TP is suspended l freni a beam |'l2 extending from the magazine |13 off the pulp grinder-fand mounts an actuatingfarm f-'Ill at i'tsilowerl end. Finger |15 extending'from operative connection totl-fe ram orpressure fooi' 'i5 (see Figure 3) is designed to engage the adjustable stop |-'I 6= or the lowerL end |-'|1 ofthe pendant arm HF. The movement oftfl'ie"v finger between the distance limits corresponding to* thel adjustlment between the stop I 16 and the lower end |11 of the pendant arm |1| determines the travel limits of the piston 24 within the cylinder I0 and therefore the extent of movement of the ramor pressure foot 25 toward and away from the grinding wheel. Referring to Figure 14, the arm |14 Aterminates in the step |13 and is slidably mounted within the housing |19 which houses the switch means 55. Housing |19 is mounted on a suitable casting ldwhich extends from the side `IBI of the pressure cylinder Ill. The switch arm |82 has a suitable roller |83 which rides in the step |18. Suitable leads |84 extending from switch means 55 for appropriate connection in the electrical circuit (shown in Figure 9).

It will be apparent that as the pressure foot 25 (see Figure 3) proceedsv .forward and ap- -proaches the end limit of its travel, that iinger will engage the lower end |11 of the pendant arm |1| thereby causing withdrawal of the arm |115 from the housing .|19 (see Figure 14) ,thereby allowing the switch arm |82 to rotate counterclockwise and providing a through circuit in switch means `55 resulting ultimately in opening of the K valve and closing of the H valve. When the pressure foot retires to the adjustable end limit vof its travels, the finger |15 will engage the stop Ht` causing the arm |14 to be thrustinto the housing '1I 1,5, the step I'Ias itpasses over the switch arm' 82 causing rotation of the latter clockwise to open the electrical circuit in the switch means 55, whereupon both the K and G 14 -is a relief 'valve (see Figures 3,-4 and 18) to lessen the power flurry' set up by logs bumping the grinding stone. The speedof advance of the piston is controlled by the I valve, by controlling any desired pressure ahead of the main piston` This back pressure may be different on all .four pockets of a conventional four-cylinder system, 'thus causing the governor tov automatically apply four different effective pressures, The four-way valve. 30,. shown in Figures 3 to 8, serves as an effective and simple means of operating the controly unit in the event that the electrical circuit of the control unit breaks down, or in halting the pressure foot 24 at any desired position when the grinding pocket'must be cleared.

In former types of hydraulic systems for driving pulp grinders where a governor was used to govern the/ load on the grinding motor by controlling the pressures appliedby various pressure feet, when a pressure foot completed its grinding operation, the pressure which it applied to the grinding stone would be suddenly released. The conventional method of releasing pressure is to cut oil' the supplyof high pressure water to the back end of the pressure cylinder behind'the piston. As a result, the total load on the grindingY motor is reduced suddenly and the governor is called upon to supply a large amount of high valves close, and the H valve opens as previously described.

In Figure 2, the piping or tubing shown interconnecting the G, H and K valves requires no description since a skilled person may follow the fluid circuit diagram of Figures 3 or 4 and connect these components to function in the desired manner. f

Although I have described a specic form of my invention, it will be appreciated that many alternatives will be apparent to skilled persons. For example, the K valve may be eliminated by a /1ono of an inch diameter orifice hydraulically in parallel with the G valve. f In the operation discussed above, it will be realized that the K valve is open when the H valve is closed. It is therefore not really necessary to employ two such valves, the advantage of including the K valve is to ensure against waste water when the H valve is open, since by the use of a` simple orifice de-` same from the raw high pressure line intothe control feeder line. I have found that when control units according to the present invention are included in a hydraulic pulp grinding system'to control the operation of the pressure cylinders, the power or load peaks have been substantially eliminated due, no doubt, in large part, to the `cushioning of .the piston of the pressure cylinder at the ends of its stroke before applying either the high pressure or the low pressure for retiring or advancing the piston. Also, by utilizing an electrical arrangement represented by the circuit diagram of Figure 9. it will be apparent that the possibility of more than the load demand required for one pressure cylinder occurring at any one time is eliminated. A pluralitv of pressure cylinders controlled bv control units according tothe present invention which are electrically v interrelated as described are actuated separately,

but the actuation of the pistons` of the pressure cylinder takes place in no predetermined order. It isalso possible, by means of the I valve, which pressure water to the remaining pressure cylinders and increase the pressures on their pressure feet to compensate for the sudden reduction of load on the grinding motor. However, I obviate this disadvantage, as it will be apparent from the above description, by gradually releasing the load applied to the grinding motor by any one pressure foot at the end of its travel due to the cushioning of the piston formerly described. This could be accomplished by gradually cutting off the supply of high pressure fluid by way of the A valve but I prefer to gradually release the load in the manner already described. VThat is to say, when the limit switch 55 is actuated the H valve is closed and the K valve is opened (see Figure 9) and therefore the E valve will close first as previously described (see Figure 3). The governed high pressure fluid in driving the piston forward after closure of the E valve works against build up of pressure in the front end of the pressure cylinder causing the load applied against` the grinding stone to be gradually reduced. This will allow the governor (see Figure 1) to compensate for the change in load and call for greater pressure to be applied on the remaining pressure feet of the system. Also where two limit switches have been tripped, one after the other, it will be lapparent that the second cannot cause actuation Aof its pressure cylinder until the rst has completed its withdrawal andvbegun Ato apply full load. It will be apparent from the former description that the secondpressure cylinder cannot be actuated until the first limit switch is actuated by the full return of the piston thereof. However, it would still be disadvantageous to allow the second pressure cylinder to retire and release its load from the grinding stone until the first is again driving under full load conditions. It is obvious for this reason therefore, that the K valve has a small orice to delay the actuation of the E valve in each case so that even when `the H valve is closed by actuation of the limit switch, the pressure cylinder will not cease applying pressure to the grinding stone for a predetermined period of time after actuation of the limit switch. The limit switch means must there- 115 fore; be-f adjusted toVg causeftlel return. of the pzf'esL sure' foot before" the magazine isv empty.

Althougir- I have shown`r the present# control unity as l deriving der-tain high-prssureffluidl from aigoiernor of the prior art, it Willbe appreciated that it isanentiiiely separateunit. Asfsuckliy control unit i`s'=capable"ofoperating satisfactorily tocontrolthe akctuation5 of av pressure cylinder Where the governed highepiiessure' terrfinal-v at Figure `lis' common' With the raw high-pressurev terminal.- In'such instance; it'vr would be desirable to employ 'some' sort ot governor in'the electrical power system driving the'f grinder motor and theipump'fmotor which may o'rmaynot-be re"- lated to the hydraulic?pressuresystem;

VariousA modificationsC may be made in the' invention wit-hout departing `from the spirit" thereoif, or the'scopeof theclaimsiand therefore; the exact-forms shown areto' beltaken' as' illustrative only, and notI in' ay limiting. sense"y and IY` desire thatI only such limitations shallf be placedA thereo'n 'as-are imposed by th'e'prior art orare-specically set forth in the' appended' claims.

What- I claimv as invention: is:

l'. In a hydraulic system' for'd'rlving thepressure* ioot" pistonsl of af plurality oi`V` pressure cylinders of a1 pulpx1 grinding 'unit in" which the hydraulic pressure supplies include, a raw highpressui-e terminal; aT governeu' high-pressure terminary a 'low-pressure"terminal, andi a' return t lineVv terminal;` a' plurality' ef `control' units; cennected hydraulically inl parallel to' said terminals; each' 'being' designed-ta control the operation of a pressure ioctpistcir of' one pressure' cylinder, and' 'including meanshydraulically" connecting the control unit to' either' end' of' the lpressure cylinder ivhich it contrlsftd apply hydraulic pressure'A to either end of'thefprssureootplston; and eiectricalnieans governing'opeation of each control' unitA including relay meansi desig-neclto be` connected electrically' inserie's with the relay means' of other 'controll units of- `said system Whereby'the' electricalE systems oli said control units so? inter-related may 'cause actua-tionof only one control uni-t and'v the pressure footpiston of its pressure cylinderat any-'one time.-

2-.y InA ahydraulic system' forV driving the pressure foot pistons oai plurality of pressure cylinders ofa pulp grinding unit inY which the hydraulic pressure supplies include,Y a raw highpressure terminal, a governedhigh-pressure terminal, alow-pressure terminaLand a returnt line terminal; a plurality of controlunits connected hydraulically in parallel to said terminals,r each being designed to control the operationof a pressure foot piston of one pressure cylinder,

-and including means hydraulically connecting the control' unit toi either ene ci tnepressure cylinder which it controls to apply hydraulic pressure to either' end of the pressure foot piston,V and electrical means governing operation of each control unitincluding` relay means designed to `be connected electrically in series with the relay' means of other'control unitsof said Vsystem whereby the electrical systems of said control units so inter-related may cause actuation of only one control unit and the pressure foot piston of its pressure cylinder' at any one time, and adjustable valve means for"` each control unit designed to control 'theV discharge of fluid from thel front endI of theV pressure cylinder in front df said piston When the latter isy advancing, whereby the grinding" pressure of the Dre'ssu're io't Amay be cohtolled independently for each pressure 3.. In a1 hydraulic' systemlor driving the' pressurefrfoot pistons ofl a plurality of: pressure` cylindeis of a'- pulp grinding: unit in which' the' hydraulic pressure suppliesv include, a raw' high'- pressure terminal; af governed high-pressure terrhinal;.y aA low-pressure' terminal.; and afreturn line'terni'inal;` a plurality of control units' conne'cted hydraulically in parallel.' to said terminals, each being' designed' to control-'the'operation of ay pressure foot piston of one pressure cylinder, and including' means hydraulically connecting the"- contro'l u'n'it tot eitherl end of the' pressure cylinder'Which-itigoverns*to apply hydraulic pres'.- surefon'leither end ofl the pressure-foot'piston, and electrical means governing operation-of eachcontrol unit including. relay means designed to be connected electrically in series with the relay means of other control unit'soi said system Whereby' the electrical' systemsl of said control units so--'inter-relatedy may-canse` actuation; of only one control unit' andi thei pressure foot piston; o'f its pressure cylinder at any one time, and valve meansl wherebyy said pluralityof valves may be manually' controlledl in; their operation in the eventT offfailure" of' said* electrical circuit;

4. Infaf hydraulic system for driving the-pressure'ffoot pistons of' av plurality of pressureN cylindex-si of a pulp-grinding.- unit inv which tlieliy- Clliaulic` pressure',` supplies include,. a4 raw highpressure"terminal; a' governed high"- pressur'e' terminal, aE low-pressure terminal-` and a return line terminal; 'ai plurality of control units connected* hydraulically in.` parallel? t`o= said terminals, each being designed to control the operation` of trol units so i'nterlrelated may cause actuation of only one control unit and the pressure foot piston of its pressure cylinder at any one time, said' plurality of valves having designations A, B, C, D, and Ereach being comprised of a body havinga pair' of chambers with a port communi'- cat'ing. between saidY chambers and a closure member designed normally toshut off communication between said chambers of the B` and D valves and normally to allow communication betWeeI-i-said chambers et the VA, C,. and valves, spring means in connection withY the closure members oi the. B C; D, andy E valves adjustable to retainthe same in their normal positions,-'one--of the-chambersot the A valve. being in: communication with saidgoverned high-pressure: terminal, the other chamber'beingin com'- mu-nication-With the rear endof said pressure cylinde-r; whereby governedhighf-prcssure is applied toithefbackfend'oi said pressure foot piston when the'closuremember of the A valve is out ofen'- g-agementv with' the" port between the' chambers thereof, spring means' designed to provide' cio'- suref of the por-trof the A valve by' said closure member info'pposltion to governed high-pressure wherebythe closuemeinler of said A valve is relieved from engagement' with" said' port' to allow communication between said' chambers' when the ll'uiolf pressure 1`n"th`e clialnber of the valve Cblliuhoalilg t' the back ild' O'f S-/d peSSlle ycylinder reaches a predetermined value according to the compression of the A valve spring.

5. In a hydraulic system for driving the pressure foot pistons of a plurality of pressure cylinders of a, pulp grinding unit in which the hydraulic pressure supplies include, a raw highpressure terminal, a governed high-pressure terminal, a low-pressure terminal, and a return line terminal; a plurality of control units connected .hydraulically in parallel to said terminals, each trol unit including relay means designed to be connected electrically lin series with the relay vmeans of other control units of said system `whereby the electrical systemsA ofxsaid control units so inter-related may cause actuation of only one control unit and the pressure foot piston of its pressure cylinder at any one time, and adjustable valve means for each control unit designed to control the discharge of iiuid from the front end of the pressure cylinder in front of said piston when the latter is advancing, whereby the grinding pressure of`the pressure foot may be controlledindependently for each pressure cylinder, and valve means whereby saidplurality of valves may be manually controlled in their operation in the event of failure of said electrical circuit.

6. In a hydraulic system for driving the pressure foot pistons of a plurality of pressure cylinders of a pulp grinding unit in which the hydraulic pressure supplies include, a raw-high pressure terminal, a governed high-pressure ter- `minal, a low-pressure terminal, and a return line terminal; a plurality of control units connected hydraulically in parallel to said terminals, each being designed to control the operation of a pressure foot piston of one pressure cylinder,- and including means hydraulically connecting the control unit to either end of the pressure cylinder which it controls to apply hydraulic pressure on either end of the pressure foot piston, electrical means governing operation of each control unit including relay means designed to be connected sure of the pressure foot mayV be controlled independently for each pressure cylinder, said plurality ofvalves having designations A, B, C, D, and E each being comprised of a body having a pair of chambers with a port communicating between said chambers and a closure member designed normally to shut oil communication between said chambers of the B and D valves and normally to allowV communication between said chambers of the A, C and E' valves, spring means in connection with the closure members of the B, C, D, and E valves designed to retain the same in their normal positions, one of the chambers of the A valve being in communication with said governed high-pressure terminal, theother 18 being in communication with the rear end of said pressure cylinder, whereby governed high-pressure is applied to the back end of said pressure ,foot piston when the closure member of the A valve isout of engagement with the port between the chambers thereof, spring means designed to vprovide closure of the port of the A valve by said .closure member in opposition to governed highvpressure whereby the closure member of said A valve is relieved from engagement with said port to allow communication between said chamber when the fluid pressure in the chamber of the A yvalve communicating to the back end of said pressure cylinder reaches a predetermined value according to the compression of the A valve spring.

' 7.Y In a hydraulic system for driving the pressure foot pistons of a plurality of pressure cylinders of a pulp grinding unit in which the hydraulic pressure supplies include, a raw highpressure terminal, a governed high-pressure terminal, a low-pressure terminaLand a return line terminal; a plurality of control units connected hydraulically in parallel to said terminals, each being designed to control the operation of a pressure foot piston of one pressure cylinder, and including means hydraulically connecting the control unit to either end of the pressure cylinder which it controls to apply hydraulic pressure on either end of the pressure foot piston, electrical means governing operation of each control unit including relay means designed to be connected electrically in series with the relay means of other control units of said system whereby the electrical systems of said control units so inter-related may cause actuation of only one control unit and the pressure foot piston oi its pressure cylinder at any one time, valve means whereby said plurality of valves may be manually controlled in their operation in the event of failure of said electrical circuit, said plurality of valves having designations A, B, C, D, and E each being comprised of a body having a pair of chambers with a port communicating between said chambers and a closure member designed normally to shut offV communication between said chambers of the B and D valves and normally to allow communication between said chambers of the A, C, and E valves, spring means in connection with the closure members of the B, C, D, and E valves designed to `retain the same in their normal positions, one of the chambers of theA valve being in communication with said governed high-pressure terminal, the other being in communication with the rear end of said pressure cylinder, whereby governed highpressure is applied to the back end of said pressure foot piston when the closure member of the A valve is out of engagement with theport between the chambers thereof, spring means designed to provide closure of the port of the A valve by said closure member in opposition to governed high-pressure whereby the closure member of said A valve is relieved from engagement with said port to allow communication between said chambers when the fluid pressure in the chamber of the A valve communicating to the back end of said pressure cylinder reaches a predetermined value according to the compression of the A valve spring.

8. In a hydraulic system for driving the pressure foot pistons of a plurality of pressure cylinders of a pulp grinding unit in which the hydraulic pressure supplies include, a raw highpressure terminal, a governed high-pressure teramg-cet minal,a low-pressure terminaL'anda return'line terminal; a plurality of vcontrol units connected hydraulically in parallel to said terminals, each v'being designed to control theoperation of a pressure foot rpiston of one pressure cylinder, and

including means hydraulically connecting the vcontroi unit to either end of the pressure cyl- 'connected electrically in vseries with the relay means of other control unitsl of said system wherebythe electrical systems of said control units so inter-related may cause actuation of vonly one controlY unit and the pressure foot piston of its pressure cylinder at any one time, adjustable valve means for each'control'unt'designed to control thedischarge" of fluid from the frontend of the pressure cylinder in-'front of said piston when the latter is advancing, whereby Vthe grinding pressureof the pressure foot may be controlled independently for each pressure cylinder, valve means whereby said plurality of valvesmay be manually controlled in their operation in the event ofrailure oi'said electrical circuit, said plurality oivalves having'designations A, B, C, D, and E each being comprised of a body having a pair of chambers 'witha port communicating between said chambers and a closure member designed normally to shut off communication between said chambers of the B and D valves and normally to allow communication between said chambers ofthe A, C, and E valves, spring means in connection with the closure members of the B, C, D, and E valves 'designed to retain the same in their normal positions, one of the chambers or the A valve being in communication with said governed high-pressure terminal, theY other being in communication with the rear end of lsaid pressure cylinder, whereby governed high-pressure is applied'to the back end of said pressure foot piston when the closure member of the A valve is out of engagement with the port between the chambers thereof, spring means designed to providev closure o' the port of the A valve-by said closure member in opposition to governed high-pressure whereby the closure member of said A valve is relieved from engagement with said port to allow communication between said chambers when the iiuid pressure in the chamber ofthe A valve communicating to the back end of said pressure cylinder reaches a predetermined value according to the compression of the Avalve spring.

9. A control unit designed to control the operation of a pressure cylinder of a pulp grinder in which the piston of said cylinder is adapted to be driven by hydraulic pressure derived from a low-pressureY line and a high-pressure line, comprising, a plurality of operatively related valve means, certain of which are in communication with the back end of said cylinder, others of whichare in communication with the front end rof said cylinder, said valve means being Vdesigned to place the front end of said cylinder in commimication with said lowepressure line to cause `means placingr said high-pressure line in com- 'mun-ication with the back end of said-cylinder to "apply highpressure to said piston when the "pressure behind? said piston approachesV a predetermined value, said' valve meanseach corn"- prising a body having upper and lower chambers and avclosure member designed to seal off communication between the upper and e lower chambers of certainl of said valves when actuated and to allow communication between the upper and lower chambers of others of said valves when actuated, the -means for providing actuation of said valves predetermined 'ordercomlprising, valve means" for communicating highpressure -fluid to-s'aid valves for actuatingthe respective closure-members, and means inconnection with-each-valve for determining the order ofactuation of-the'closure member thereof.

10. A control unit designed to control the operation of a pressure cylinder of a pulp grinder in which thepiston of said cylinder is adapted to be driven by'hydraulicv-pressure derived from a `low-pressure linelanda high-pressure line, comprising, al plurality of operatively related valve means, certain of which are Ain communication with the back end of said cylinder, others of whichv are in communication with 'the front endY of said cylinder,-said valve means being designed to place the front end of saidfcylinder in communication with said low-pressure line to cause a retiring-o the piston in-said cylinder, means for providing actuation --of said plurality of valves in predetermined order to urge said piston forward afterfit has'completed its retiring stroke, means placing said high-pressure line in communication with the back Vend-of said cyliner to apply high-pressure to said piston when the pressure behind said pistonY approaches a predetermined value, said valve means each comprising a body having upper -and lower chambers and a closure member'designed to seal off communication between the upper and lower chambers of certain of said valves when actuated and to allow communication between the upper and lower chambers of Yothers of said valves when actuated, the means-for providing actuation of said valves in predetermined order comprising, magnetic valve means for communicating vhighpressure uid to said valvesfor actuating the respective kclosure members, and spring means in connection with'each valve for'determining the order of actuation of they Iclosure'member thereof, said magnetic valve vmea-ns comprising at least Ytwo electrically controlled magnetic valves, one

of which is designed to place'said operatively related valve means in communication'with said high-pressure line whensaid piston is retiring, the other of said 'electrically controlled magnetic valves being designed to place saidplurality of valves in communication'with aV return line when said piston Yis retiring whereby the closure`-mem bers of said plurality `ofvalves assume a normal position.

l1. A control unit designed" to control the operation of a pressure cylinder of a pulp grinder in which the-piston of said cylinder is adapted to be-driven by hydraulic pressure derived from a low-pressure line and a high-pressure line, comprising, a plurality of operativelyv related valve means, certainY of which are in communication with the backendof-sai'd cylinder, others of which are in communication with the front end of said cylinder, said valve Vmeans `being designed to place the frontendfof said cylinder in communcationwith said ,low-'pressure' line to cause a retiring of the*pistoninv said cylinder, means for 'providingk actuation v'of said plurality or valves in predemrnne'd-order to' 'urge said piston 4forward after it has completed'i'ts retiring stroke,

means placing said high-pressure line in communication with the back end of said cylinder to apply high-pressure to said piston when the pressure behind said piston approaches a predetermined value, said valve means each comprising a body having upper and lower chambers and a closure member designed to seal off communication between the upper and lower chambers of certain of said valves when actuated and to allow communication between the upper and lower chambers of others of said valves when actuated, the means for providing actuation of said valves in predetermined order comprising, magnetic valve means for communicating high-pressure uid to said valves for actuating the respective closure members and spring means in connection with each valve for determining the order of actuationv of the closure member thereof, said magnetic valve means comprising at least two electrically controlled magnetic valves, one of which is designed to place said operatively re-V to be driven by hydraulic pressure derived from` a low-pressure line and a high-pressure line, comprising, a plurality of operatively related valve means, certain of which are in communication with the back end of said cylinder, others of which are in communication with the front end of said cylinder, said valve means being designed `to place the front end of said cylinder in communication with said low-pressure line to cause a retiring of the piston in said cylinder, means for providing actuation of said plurality of valves in predetermined order to urge said ypiston forward after it has completed its retiring stroke, means placing said high-pressure line in communication with the back end of said cylinder to apply high-pressure to said piston when the pressure behind said piston approaches a predetermined value, said valve means each comprising a body having upper and lower chambers and a closure member designed to seal ofi communication between the upper and lower chambers of certain of said valves when actuated and to allow communication between the upper and lower chambers of others of said valves when actuated, means for providing actuation of said valves in predetermined order comprising magnetic valve means for communicating highpressure Iiuid to said valves for actuating the respective closure members and spring means in connection with each valve for determining the order of actuation of the closure member thereof, said magnetic valve means comprising at least two electrically controlled magnetic valves, one of which is designed to place said operatively related valve means in communication with said high-pressure line, when said piston is retiring, the other of said electrically controlled magnetic valves being designed to place said plurality of valves in communication with a return line when said piston is retiring whereby the closure members of said plurality of valves assume anormal position, and limit switch means actuablev by said piston governing operation of said magnetic valves, and relay means in electrical circuit connection with said limit switch means designed to be connected electrically in series through the relay means of another control unit whereby only one limit switch means may cause actuation of its control unit at any one time, a plurality of control units so related controlling actuation of pressure cylinders in no predetermined order.

LORNE A. COLE.

REFERENCES CITED The following references are of record inthe 

